Yes, I had exactly the same problems when I upgraded to 2.2. My signal was very erratic after updating.
I also had the same issue with the Sat Nav... I first noticed it when I drove down south for a couple of hours and after the first hour of the journey the device announced 'Satellite signal lost'. At first I thought it was one of those things and that it would return shortly, however, it never did
. Furthermore, I also noticed that it had taken the cell signal with it! When I checked the back of the device it was pretty hot and instantly figured that it was overheating.
Sure enough after half an hour on standby it all came back to life again, but on our return journey it did the same thing after only half an hour or so.
At this point I was pretty disheartened and thought that I was going to have to return it, but, having flashed phone ROMs in the past I know that it's usually a good idea to hard reset a couple of times after flashing so that the EPROM is reprogrammed correctly. I did this (despite the ball ache of having to reconfigure everything!) and instantly noticed some subtle differences (like Facebook app had changed slightly etc). Since this the radio signal seems to be better, although it is still a little erratic compared to 2.1. It also seems to have cured the SatNav signal drop out/overheating as I have done a couple of 4 hour + trips and although it did drop on one occasion very briefly, it seems to have resolved it. Having said this, the unit still gets pretty warm and I personally believe that this handset has a design fault with regard to overheating (why didn't they make the back out of metal like the Legend which would act as a heat sink?).
One more thing to throw in the pot is that prior to my hard reset I was using 'Advanced Task Killer' and I had my suspicions that this may have been causing some resource issues and contributing to the overheating. As I have not reinstalled it since I could not say for sure, but there certainly seems to be a lot of controversy about whether it's a good idea to use it...
Hope this helps,
G